This invention relates to a method and apparatus for depositing flowable material onto a surface by locating the particular position on the surface to which the material is to be deposited and thereafter depositing a metered dosage of the material at that particular position.
The method and apparatus of the present invention are particularly applicable for depositing equal dots of adhesive onto particular surface portions of a circuit board regardless of surface variations in the circuit board due to such things as warpage.
Prior art attempts to locate particular surface points in spaced relation to a dispensing nozzle tip having included vision systems at least an order of magnitude greater in cost than the instant invention.
A prior art attempt at solving the problem of board warpage included a depth stop located near the dispensing nozzle to regulate spacing between the nozzle and the board. However, surface variations could and did occur between the depth stop and the particular point on the surface to which the adhesive dot was to be dispensed, resulting in a lesser or greater spacing between the nozzle tip and surface and a respectively smaller or larger dot size. This approach also presented a bigger "footprint" in that the depth stop limited the closeness to which the adhesive dot could be applied to surrounding, previously applied components.
Accordingly, it is an object of the invention to minimize the footprint of the apparatus of the instant invention to that of the tip of the nozzle itself.
It is another object of the invention to sense a particular position on the surface of the circuit board and accurately space the dispensing tip therefrom, regardless of board warpage, for repeatable dispensing of a flowable material dose, such as a dot of adhesive.
Still further, it is an object of the invention to provide for dosage metering of the flowable material by sensing the material during depositing thereof.
Additionally, it is an object of the invention to sense engagement of the onset of the dose with the surface onto which it is dispensed in order to control the dosage.
In a preferred embodiment of the invention, a dispensing nozzle tip is advanced into engagement with the particular position of the circuit board to which material is to be applied while the reactive force on the nozzle tip from the circuit board is sensed by variation in the output from a load cell such that an exact spacing may be provided between the nozzle tip and that portion of the surface to which material is to be dispensed. Having provided such spacing between the tip and surface, the flowable material, in this case adhesive utilized to hold the subsequently applied surface mounted components onto the circuit board, is dispensed and a reactive force from the surface is again sensed by the load cell arrangement via the flowable material itself. Surface location and dispensed dosage sensing is performed for every dose of material to be applied.